Experimental investigation on the behavior of GFRP-RAC-steel double-skin tubular columns under axial compression

The glass fiber-reinforced polymer (GFRP)-recycled aggregate concrete (RAC)-steel double-skin tubular column (DSTC) combines and optimizes the benefits of the fiber-reinforced polymer (FRP)-concrete-steel DSTC, and RAC. To study the axial compressive behavior of the GFRP-RAC-steel DSTC, tests on ten column specimens which consider the difference of the replacement percentage of the recycled coarse aggregate (RCA), the concrete strength and the thickness of the GFRP tube were conducted. The failure mode, ultimate load, confinement factor, load-longitudinal curve, ductility, and stress-strain curve were analyzed and discussed. In addition, the theoretical formulae to estimate the ultimate load of the GFRP-RAC-steel DSTC were derived. The results showed that (1) the development of the lateral expansion of the concrete led to the hoop rupture of the GFRP tubes and the inward buckling of the inner steel tube; (2) the natural aggregate concrete (NAC) in the traditional DSTC can be replaced with RAC and the strength can be guaranteed, and a GFRP-RAC-steel DSTC specimen with a 50% replacement percentage of the RCA was recommended; (3) the theoretical results agreed well with the experimental results. The application of RAC to the DSTC can utilize these materials effectively and make a contribution to the economic development and environmental protection.